The present invention relates generally to an improved pushbutton device for actuating the electropneumatic parking brake (EPH) of a vehicle.
An electropneumatic parking brake of the general type under consideration is described in DE 10336611 A1. The EPH is used to safely hold a vehicle, especially a commercial vehicle having a pneumatic brake system, during a prolonged stoppage by venting a spring-actuated brake cylinder. By venting the spring-actuated brake cylinder, the brakes, usually of the rear axle, are applied and held without additional energy input. For this purpose, the vehicle can be equipped with an electronically activated brake system (EBS) or even with a brake system that is conventionally activated via pneumatic control pressure.
To actuate the parking brake function, the known pressurized fluid operated brake system of a vehicle is provided with an electric parking brake signal transducer, which is designed as a pushbutton with three positions: neutral, parking brake and trailer checking. The detection of faults, such as contact faults or wire breaks of the signal transducer, as may be required by applicable legal regulations, is possible to only a limited extent.
DE 19838886 A1 describes an electric parking brake (EPB), which can be actuated with an operating element for parking a vehicle. Upon actuation of the operating element while the vehicle is stationary, the electric parking brake is alternately applied and released. The operating element is designed as a pushbutton with two positions and one status indicator. Fault checking of the operating element is not addressed.
WO 00/29268 describes a device and method for controlling an electrically actuated parking brake. For particularly reliable detection of the operator's command to actuate the parking brake, the input device for receiving the operator's command is redundantly designed in its individual components and, at the same time, monitored by means of an electronic control device. For this purpose, a plurality of procedures takes place cyclically within an evaluating unit of the control device in order to permit detection of a fault in the input device and also to ensure that the operator's command can be recognized. This way, it is possible to react appropriately to faults that occur and, alternatively, to place the vehicle in a safe driving condition by means of the parking brake even if the operator's command is not clearly recognized. For this purpose, fault detection is made possible by measuring potentials across resistors installed in the input device. A fault is indicated by a signaling device in the dashboard.
The known input device has considerable cabling complexity, namely eight connecting lines. Furthermore, it has a complex construction of switches and resistors and a complex evaluation method for detecting a fault. Considerable memory space is needed by the program routines in the evaluating microcontroller.